SAMFAQ

SAM Frequently Asked Questions

Q1. Can the FGM-3h magnetic sensor be used with the SAM?

A1. Yes, the -3h sensor can be used with the SAM and is entirely compatible with it. However, there are at least a couple considerations:
(1) It is possible to saturate the -3h sensor, even without a geomagnetic storm, depending on the sensor orientation and location. The -3h can be swamped when it's aligned N-S in most locations. Geomagnetic storms will further compound the problem. For example, let us use Melbourne Australia as an example. Using the online geomagnetic calculator at the NGDC, the N-S component at Melbourne is ~21,000 nT and the E-W component is ~4,400 nT. At that location, the -3h would be saturated if it is oriented in the N-S plane, but it might be suitable if it is oriented in the E-W plane. However, we question whether anything will be gained by using the -3h. See also next question.
(2) Even though the local ambient magnetic induction at your location is within range of the -3h, it may be saturated by normal or stormy geomagnetic activity. When saturated, the sensor becomes non-linear and its output signal is no longer proportional to the magnetic induction.

Q2. What are the resolutions of the FGM-3 and -3h sensors?

A2. The resolutions of the -3 and -3h are the same, around 1-2 nT. The -3h signal output characteristics are the same as the -3 and is compatible with the SAM. However, you will need to adjust the offset and correction in SAM_INI so that your data values are of the correct magnitude.

Q3. Is the FGM-3h sensor available as an option?

A3. The FGM-3h sensor is not listed in the price list but is available as an option. Please contact us for price and availability.

Q4. Does the magnetic sensor require a separate power supply?

A4. You do not need a separate power supply for the sensor. The same +12 vdc power supply that runs the main controller also runs the sensors. Note that the kit does not come with an ac adapter power supply but one is available as an option for North America. In almost all SAM systems, the sensor is powered from the main controller through a 3- or 4-conductor cable, (1) lead for common ground, (1) lead for power and (1) lead for each sensor output signal.
In one of our systems, we removed the sensor 5 v regulator on the main controller and connected the +12 v main controller input voltage to the sensor cable (this is very simple and requires only one small jumper). At the sensor, we installed a 78L05 voltage regulator and four filter capacitors on the regulator, two on the input and two on the output, for noise control.
If you leave the 5 v regulator on the main controller, you still can power the sensor but you may have a voltage drop problem if the sensor is located too far away. We have done quite a bit of experimenting with the sensor and found that it is not particularly voltage sensitive. However, the datasheet says the operating range is 4.5 - 5.5 v so it is best to stick with that criteria. There is some discussion of this in the SAM construction manual..

Q5. How many sensors does the SAM support?

A5. The original SAM hardware and software fully supports two sensors. The SAM-III released in 2010 supports three sensors. The original SAM main controller PCB has space for the logic circuits associated with a third sensor. A conversion kit is available.

Q6. Can the sensors be mounted anywhere?

A6. The sensors can be mounted anywhere as long as they are away from artificial magnetic fields. However, there are a number of considerations, three of which are described here. For additional information, download the SAM Construction Manual:
    (1) The magnetic sensor temperature sensitivity must be taken into account. There is considerable discussion on this in the construction manual. One way around the temperature drift problem is to bury the sensor in earth. So far, we have found it is impractical to automatically correct the sensor output for temperature drift. However, the SAM does support an external temperature sensor that can be collocated with the magnetic sensor. This mainly would be used to let you know if a temperature transient caused what looks like a magnetic transient. We have not tested this feature yet and presently do not support it but can provide information so you can experiment on your own.
    (2) The magnetic sensor will pickup any variation in the local magnetic field including automobiles moving in the area, ferromagnetic tools brought nearby and other manmade magnetic disturbances. Therefore, the sensor should be placed in a magnetically quiet location.
    (3) In a 2-sensor installation, the sensors may interact with each other if they are mounted too close together. Refer to the next question.

Q7. In a 2- or 3-sensor installation, do the sensors require separation?

A7. The following information was provided by Darrel Emerson, who performed some undocumented testing on the FGM-3 sensors. If two sensors are parallel and too close, they tend to pull each other onto the same frequency. In the parallel configuration, it is recommended that the sensors be separated by at least 150 mm (6 in.) to minimize this effect. If the two sensors are at right angles to each other, the pulling effect is much smaller. The effect also depends on the alignment with the Earth's field. If the sensors are parallel, but one is rotated 180 degrees (so the pins are pointed in opposite directions), then for most alignments with respect to the Earth's field, the two sensor frequencies are quite different, and the pulling effect disappears. However, when their alignment with the Earth's field brings them both to nearly the same frequency, the frequency pulling effect is strong. Users are encouraged to perform their own experimentation and report their results to the SAM-International Yahoo Group.

Q8. How much does the SAM cost?

A8. Click here for a price list and ordering information.